Fixes CVE-2021-4034, local privilege escalation with 'pkexec':

  https://www.openwall.com/lists/oss-security/2022/01/25/11

Patch from <https://gitlab.freedesktop.org/polkit/polkit/-/commit/a2bf5c9c83b6ae46cbd5c779d3055bff81ded683>.

From a2bf5c9c83b6ae46cbd5c779d3055bff81ded683 Mon Sep 17 00:00:00 2001
From: Jan Rybar <jrybar@redhat.com>
Date: Tue, 25 Jan 2022 17:21:46 +0000
Subject: [PATCH] pkexec: local privilege escalation (CVE-2021-4034)

---
 src/programs/pkcheck.c |  5 +++++
 src/programs/pkexec.c  | 23 ++++++++++++++++++++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/src/programs/pkcheck.c b/src/programs/pkcheck.c
index f1bb4e1..768525c 100644
--- a/src/programs/pkcheck.c
+++ b/src/programs/pkcheck.c
@@ -363,6 +363,11 @@ main (int argc, char *argv[])
   local_agent_handle = NULL;
   ret = 126;
 
+  if (argc < 1)
+    {
+      exit(126);
+    }
+
   /* Disable remote file access from GIO. */
   setenv ("GIO_USE_VFS", "local", 1);
 
diff --git a/src/programs/pkexec.c b/src/programs/pkexec.c
index 7698c5c..84e5ef6 100644
--- a/src/programs/pkexec.c
+++ b/src/programs/pkexec.c
@@ -488,6 +488,15 @@ main (int argc, char *argv[])
   pid_t pid_of_caller;
   gpointer local_agent_handle;
 
+
+  /*
+   * If 'pkexec' is called THIS wrong, someone's probably evil-doing. Don't be nice, just bail out.
+   */
+  if (argc<1)
+    {
+      exit(127);
+    }
+
   ret = 127;
   authority = NULL;
   subject = NULL;
@@ -614,10 +623,10 @@ main (int argc, char *argv[])
 
       path = g_strdup (pwstruct.pw_shell);
       if (!path)
-	{
+        {
           g_printerr ("No shell configured or error retrieving pw_shell\n");
           goto out;
-	}
+        }
       /* If you change this, be sure to change the if (!command_line)
 	 case below too */
       command_line = g_strdup (path);
@@ -636,7 +645,15 @@ main (int argc, char *argv[])
           goto out;
         }
       g_free (path);
-      argv[n] = path = s;
+      path = s;
+
+      /* argc<2 and pkexec runs just shell, argv is guaranteed to be null-terminated.
+       * /-less shell shouldn't happen, but let's be defensive and don't write to null-termination
+       */
+      if (argv[n] != NULL)
+      {
+        argv[n] = path;
+      }
     }
   if (access (path, F_OK) != 0)
     {
